It is proposed to investigate the endocrine aspects of calcium homeostasis along the following lines: (1) a study of the regulation of the renal-vitamin D endocrine system in the Japanese quail, particularly in the reproductively active female; (2) a survey of the plasma gonadal hormone (androgen, estrogen, and the progesterone) levels in the Japanese quail of both sexes and at all stages of development; and (3) a qualitative and quantitative study of the bioassayable parathyroid hormone-like material in urines from patients with hyperparathyroidism and hypercalcemia of cancer.